PAINT DRYING 1 -7 PAINT DRYING The process in which a liquid-like paint is hardened and forms a hard coat is called drying. Different components of the paint follow different processes during drying. · Solvents and thinners evaporate into the air and do not remain in the coat. · Pigments remain unchanged as powders, as before application, and stay in the coat. · Liquid resins in the paint change into hard solids after drying. In other words, drying is a process of the paint in which resins are hardened and form a film. II Drying rl Solvent evaporation (air drying) I m I ~ ri'H_e_a_t_p_o_l_y_m_e_r-iz_a_t-io_n_(b_a_k_i-ng-) 1 Paints may be dried in one of the two types:
--1~ _______ R_e_a_c_t_io_n _______ ~~ Dual-component polymerization 1. SOLVENT EVAPORATION (AIR DRYING) This type of paints forms a coat when the solvent and thinner in them evaporate. Resins remain unchanged after the formation of the coat. Therefore, the hardened coat can be wiped off easily with a thinner. Solvent evaporating paints for automobiles include the following:
· NC lacquer (nitrocellulose lacquer) · NC acrylic lacquer (nitrocellulose acrylic lacquer) · CAB acrylic lacquer (cellulose acetate butyrate acrylic lacquer) In comparison with the reaction type paints, the solvent evaporation type paints are less resistant against solvents and weathering, but they are sometimes preferred because of their quick drying and better workability. Solvent and Thinner Evaporate During Drying DRYING PROCESS OF SOLVENT EVAPORATION TYPE PAINTS -9-